1. Field of the Invention
This invention relates to the fabrication of diamond nanopillars. The invention also relates to diamond nanopillar arrays.
2. Background Information
Due to its unique combination of outstanding physical and chemical properties, such as wide band-gap, chemical inertness, the highest hardness and thermal conductivity, negative electron affinity, and biocompatibility, diamond is considered to be a promising material for application in electronic and micro-electromechanical devices, biomedical sensors and electrochemical electrodes, and field electron emission (FEE) devices. Diamond can be synthesized in bulk crystalline forms using a high-pressure and high-temperature method and in film forms employing chemical vapor deposition (CVD), typically in a hydrogen environment (including plasma) with a carbon precursor. Highly-oriented diamond films have been available and prepared on various substrates using bias-enhanced nucleation (BEN) and by controlling the growth parameters. Nanocrystalline diamond (nano-D) films have recently attracted considerable interest as they overcome the great surface roughness which is a consequence of the faceted morphology of polycrystalline diamond films, but retain to a large extent the extreme properties of polycrystalline diamond films.
The application of diamond in the electrochemistry and biomedical fields has attracted increasing research interest, such as in chemically inert biochemical micro-reactors and ultra-low friction micro-electromechanical sensors. Diamond is known as a biocompatible material, consisting of only carbon atoms. Compared with other electrode materials, such as gold, platinum or glassy carbon, the diamond electrode exhibits a low and stable voltammetric and amperometric background current, leading to an enhanced signal-to-background ratio (S/B), weak adsorption of polar molecules, a wide electrochemical potential window in aqueous media, long-term response stability, and great fouling resistance and chemical inertness. The superior properties of a diamond electrode make it ideally suited for in vitro or in vivo biomedical applications in chemically aggressive environments.
The potential applications of diamond depend not only on its intrinsic properties, but also on the surface geometries in which it appears. The surface functionalization of nanostructured diamond is widely recognized as a viable approach to extend and/or enhance its applications. In particular, increasing the surface area may improve the efficiency and sensitivity in electrode and sensor applications, which could open new frontiers in electro-analysis and stable biosensor. For example, a diamond pillar structure has application as two-dimensional photonic band-gap crystals for use in the near-infrared wavelength region, due to the high transparency and large refractive index of diamond in the undoped state. However, the extreme properties of diamond make it difficult to structure to a desired geometry to fully explore its advantages in different applications.
Single crystalline diamond cones with small tip radius and defined crystal orientation have been fabricated by utilizing reactive ion etching method [Lee Shuit-Tong, et al., U.S. Pat. No. 6,902,716]. Diamond pillars/cylinders have been synthesized by introducing an anodized porous alumina mold in CVD process. The diamond nanopillars formed have a uniform diameter of about 300 nm [H. Masuda, T. Yanagishita, K. Yasui, K. Nishio, L Yagi, T. N. Rao, A. Fujishima, Adv. Mater., vol. 13, pps. 247-249, “Synthesis of well-aligned diamond nanocylinders”, 2001]. Moreover, single crystalline diamond nanorods with a diameter of 50-200 nm have also been constructed from single crystalline diamond whisker by using reactive ion etching [Y. Ando, Y. Nishibayashi, A. Sawabe, Diamond. Relat. Mater., vol. 13, pps. 633-637, “Nano-rods of single crystalline diamond”, 2004].